JPH0617513B2 - Method for flattening annealing of unidirectional silicon steel sheet with excellent magnetic properties and coating adhesion - Google Patents

Description

The present invention relates to a method for flattening and annealing a unidirectional silicon steel sheet having excellent magnetic properties and coating adhesion.

[Conventional technology]

A unidirectional silicon steel sheet having a secondary recrystallization texture composed of (110) (001) orientation that is easily magnetized in the rolling direction is a transformer,
It is used as a material for generators, etc., but is industrially manufactured by the following method. That is, a molten steel having an appropriate component is obtained by a converter method, an electric furnace method, etc., and continuously cast into a slab: a hot rolled sheet is obtained by heating and hot rolling the slab. Perform pickling or hot-rolled sheet annealing, if any: further cold-rolled sheet to final thickness after one cold rolling or two or more cold rolling steps with intermediate annealing, decarburization annealing and secondary Annealing at a temperature high enough to cause recrystallization: The coil after this high-temperature finish annealing is heated in a continuous annealing furnace to straighten (flatten) the curl caused by the coiled annealing and at the same time coating for insulating coating. It is manufactured by applying a liquid, drying and baking.

In these series of manufacturing steps, the development of secondary recrystallization consisting of (110) [001] orientation, which is easily magnetized in the rolling direction, is completed by the high-temperature finishing annealing, which is the step immediately before the flattening annealing. The function of chemical annealing depends on (1) shape correction by appropriate temperature and tension (2) plastic strain associated with shape correction, cooling strain during high temperature finish annealing, bending during unwinding after high temperature finish annealing, etc. Release of strain (3) The application of a tension effect to the steel sheet by drying and baking the coating liquid for insulating coating, which has a great influence on the magnetic properties of the grain-oriented silicon steel sheet.

In the conventional flattening annealing, a coating liquid for an insulating film is applied to a steel sheet before the flattening annealing is performed, and the baking, shape correction and strain relief are simultaneously performed. For example, in Japanese Examined Patent Publication No. 53-262981, a coating solution is applied and bake annealing is performed at 800 to 850 ° C. By the way, a coating liquid for an insulating film which gives a tensile effect and an insulating property to a unidirectional silicon steel sheet is disclosed in, for example, JP-A-53-28375.
As shown in Japanese Patent Publication, the main component is phosphate,
The forsterite coating formed by the high temperature finish annealing is locally eroded by the reaction of the insulating coating liquid with the phosphate or free phosphoric acid, and the adhesion of the coating may deteriorate after the flattening annealing.

In the conventional flattening annealing, as described above, the shape correction, strain relief and baking of the insulating coating are performed at the same time, which has some effect, but the improvement of coating adhesion and effective The actual situation is that further study is required to improve and stabilize the magnetic properties by imparting various film tensions and sufficiently releasing strain.

[Problems to be solved by the invention]

An object of the present invention is to provide a flattening annealing method for a unidirectional silicon steel sheet having excellent magnetic properties and coating adhesion.

The present inventors have studied in detail the planarization annealing method in order to improve and stabilize magnetic properties and coating adhesion. As a result, the most preferable flattening annealing method is to perform shape correction, release of strain, drying and baking of the insulating coating solution, and baking the insulating coating solution applies tension to the unidirectional silicon steel sheet. It has been found that it is important to carry out at a temperature below the Curie point under given conditions.

That is, the flattening annealing corrects coil winding, cooling strain, and the like, so that plastic deformation is inevitably generated. However, if the strain generated by this plastic deformation remains, the magnetic properties are significantly deteriorated. Therefore, in order to correct the shape and release the strain by continuous annealing, the unidirectional silicon steel sheet has a large extensibility and the strain is also released. It must be heated to a temperature above 750 ° C., which is carried out in a short time. However, in this temperature range, the applied coating liquid for insulating coating has been baked to complete vitrification, and when plastic deformation is applied to the unidirectional silicon steel sheet having the vitrified insulating coating, fine cracks are formed in the insulating coating. Was found to significantly reduce the tension effect of the coating. Further, the higher the flattening annealing temperature and the longer the soaking time, the more the reaction between phosphoric acid, which is the main component of the insulating coating solution, and the forsterite coating proceeds, and the coating adhesion deteriorates.

To solve these problems all at once and further improve the magnetic properties, a coil-shaped high-temperature finish-annealed unidirectional silicon steel plate is passed through the plate at a temperature of 750 ° C. or higher to correct the shape and prevent distortion. After releasing, after applying the coating liquid for insulating coating and applying tension to the steel plate, 350 ° C or higher,
It is to form an insulating coating by baking at a temperature below the Curie point.

[Means for solving problems]

 The present invention will be described in detail below.

In the unidirectional silicon steel sheet to which the present invention is applied, it is not necessary to specify the steel composition and the manufacturing conditions until flattening annealing, and for example, C = 0.03 to 0.10%, Si = 2.0 to.
4.0%, known inhibitors such as AlN, MnS, MnSe, and BN are appropriately used, and Cu, Sn, and N are used as necessary.
Elements such as i, Mo and P are contained.

Silicon steel slab is hot-rolled, hot-rolled sheet is annealed if necessary, and is cold-rolled once or twice with intermediate annealing to obtain the final sheet thickness. Is applied and high temperature finish annealing is performed in a coil shape. After that, flattening annealing is performed.

In flattening annealing, it is disadvantageous in terms of thermal energy to perform shape correction and strain relief and baking of the coating for the insulating film independently, but in the present invention, as a result of essentially elucidating each function , In order to make the best use of the characteristics of the unidirectional silicon steel sheet which is a magnetic material and to improve and stabilize the basic magnetic characteristics and the coating adhesion, they are independently performed.

First, in order to correct the shape of the coil-shaped high-temperature finish-annealed unidirectional silicon steel sheet and release the strain, the unidirectional silicon steel sheet is passed in a plate shape at a temperature of 750 ° C. or higher. At this time, the coating liquid for insulating coating is not applied to the steel plate before annealing. The reason why the plate is passed at a temperature of 750 ° C. or higher is to perform shape correction and strain relief effectively in a short time. This plate, which is performed without applying the coating liquid for the insulating coating, does not form an insulating coating, and therefore has a low deformation resistance, and the present condition is corrected and the strain is sufficiently released, so that the magnetic characteristics are excellent.

For example, FIG. 1 shows the relationship between the presence or absence of an insulating coating under constant tension and the elongation and holding temperature of a unidirectional silicon steel sheet. The thickness of the sample steel sheet investigated was 0.35 mm.
Then, the tension was set to 0.50 kg / mm ² . Without the insulating coating, the tensile force is lower and the elongation required for shape correction is given, so that the strain can be released efficiently in a short time.

After rectifying the shape and releasing the strain, the unidirectional silicon steel sheet cooled to a temperature suitable for applying the coating liquid for the insulating coating, the coating liquid for the insulating coating, such as phosphoric acid, aluminum phosphate, magnesium phosphate, zinc phosphate, 0.3 to 1.5 kg of steel plate is coated with a coating liquid for insulating coating, which appropriately contains phosphates such as calcium phosphate, chromates such as chromic acid and magnesium chromate, dichromates, colloidal silica, etc. 350 with a tension of / mm ^{2 applied}
Baking in a temperature range of ℃ or more and less than Curie point to form an insulating film. Forming an insulating coating in a temperature range below the Curie point, that is, in a state where the magnetic domain is subdivided by applying tension to the unidirectional silicon steel sheet that is a magnetic material, remarkably improves iron loss. If the temperature is lower than the Curie temperature, the unidirectional silicon steel sheet has a low extensibility, and being able to apply a larger tension to the steel sheet is effective in improving iron loss. At the same time, low-temperature baking suppresses the progress of the reaction between phosphoric acid and the forsterite coating, greatly reducing the deterioration of the adhesion of the forsterite coating.

Next, the reasons for limiting the baking temperature of the coating liquid in forming the insulating film (vitrification) will be described. In order to significantly improve the iron loss, it is essential that the insulating coating is formed in a temperature range where the unidirectional silicon steel sheet has a characteristic as a magnetic material, and the baking temperature must be lower than the Curie point. At temperatures above the Curie point, the yield point of the grain-oriented silicon steel sheet decreases significantly, causing plastic deformation with low tension, and further increasing the reaction rate between phosphoric acid and forsterite coatings. This is the reason why it is less than the point. Since the phosphate-based coating liquid for insulating coating does not vitrify below 350 ° C, the baking temperature was set to 350 ° C as the lower limit.

Further, when the tension applied to the unidirectional silicon steel sheet during the formation of the insulating coating is less than 0.3 kg / mm ² in the above-mentioned temperature range, the magnetic domain subdivision effect is small and the iron loss is little improved, while when it is too large, plastic deformation As a result, the iron loss deteriorates and the upper limit is 5 kg / mm ² . Therefore, the desirable tension range is 0.3
~ 5 kg / mm ² .

<Example> C: 0.070% by weight, Si: 3.25%, Mn: 0.060%, S;
026%, Al; 0.030%, N; 0.0080%, Sn: 0.080%, C
u; hot rolled steel slab consisting of 0.075% by known method
After annealing-cold rolling to a final plate thickness of 0.23 mm, decarburization annealing-annealing separation agent application-final finishing annealing was performed to obtain a test coil. This coil is 850 ℃ for 60 seconds, the tension is 0.3
Heat flattening treatment was performed while applying kg / mm ² . After that, a tension-imparting coating liquid consisting of aluminum phosphate-colloidal silica-chromic acid as disclosed in JP-B-53-28375 is applied so that the weight after coating and drying is 5 g / m ^2, and condition A: 600. The film was subjected to coating baking treatment at 30 ° C. (tension applied to the steel plate of 1.2 kg / mm ² ) and B condition: 700 ° C. (tension applied to the steel plate of 0.7 kg / mm ² ) for 30 seconds. In addition, after applying the coating agent using a part of the same coil after finish annealing as a comparative material, 850 ° C.
A sample of heat flattening treatment by a conventional method of performing heat flattening and baking treatment for 60 ″ was prepared.

Table 1 shows the results of the adhesion test of magnetism and coating after the heat flattening treatment. With the material of the method of the present invention, excellent results were obtained in both magnetic properties and coating adhesion, as compared with the comparative material in which conventional coating baking treatment and heat flattening treatment were performed at high temperature.

(Effects of the Invention) As described above, the present invention, when flattening and annealing a unidirectional silicon steel sheet, corrects the shape and releases the strain before applying the insulating coating solution, and then the tension-imparting insulating coating solution. Is applied and tension is applied to form a baked insulating coating, so that the strain is sufficiently released, the insulating coating does not deteriorate, and the insulating coating has excellent magnetic properties and adhesion. Is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the presence or absence of an insulating coating on the elongation when a unidirectional silicon steel sheet is heated.

Claims (1)

[Claims] 1. When flattening and annealing a unidirectional silicon steel sheet, the coil-shaped high-temperature finish-annealed unidirectional silicon steel sheet is heated to a temperature of 750 ° C. or higher while continuously passing in a plate shape. Shape correction and strain relief are performed, and after cooling, a tension-applying insulating coating solution is applied, and the steel sheet is tensioned and baked at a temperature of 350 ° C or higher and lower than the Curie point to form an insulating coating. A method for flattening and annealing a unidirectional silicon steel sheet having excellent magnetic properties and coating adhesion.